Photocomposing machine



Jan. 11, 1955 "w. F. c. FERGUSON ETAL 2,699,101

PHOTOCOMPOSING MACHINE 2 Sheets-Sheet l Filed Sept.v l, 1950 vinili Jan.11, 1955 w. c. FERGUSON ET AL 2,699,101

PHOTOCOMPOSING MACHINE 2 Sheets-Sheet 2 Filed Sept. l, 1950 INVENTORS jUnited States Patent Oce 2,699,101 Patented Jan. 11,I 1955 PHOTOCOMPOSING MACHINE Walter F. C. Ferguson, West Orange, N. J., and John H. Greig,New York, N. Y., assignors to Mergenthaler Linotype Company, acorporation of New York Application September 1, 1950, Serial No.182,854 z claims. (ci. 9s-4.5)

This invention relates to photocomposing machines, that is to say,machines wherein images of selected characters are projected opticallyonto a photographic mem- In many machines of this type, it has beencustomary to employ character arrays consisting of either a plurality ofopaque characters arranged on a translucent background, or a pluralityof translucent characters arranged on an opaque background. In view ofthe wide range assortment of characters necessarily employed in thecomposition of type for printing, one of the diiiiculties encountered inthe design of such machines is the problem of projecting any desiredcharacter of the array'onto the photographic member in focus at thecenter of the optical axis in order that each character composed will bealigned with respect to all the other characters of the sequence.Generally speaking, only that particular character of the array locatedalong the optical axis will be so properly projected.

Various solutions to this problem have already been proposed. Oneproposed solution was to arrange the characters around the periphery ofa revolving drum and to instantaneously project the selected characteronto the photographic member as it passes the axis of the opticalsystem. Another proposal was to arrange the characters in vertical andhorizontal rows on a shiftable plate and provide mechanism to move theplate vertically and horizontally in a plane to bring any individualcharacter into the optical axis or, in the alternative, to move theoptical system with respect to the character plate to accomplish thesame result. Still another proposal was to provide each individualcharacter of the array with a separate optical system. The foregoingproposals, While all mechanically or optically feasible, are entirelyunsatisfactory due primarily to the costly, cumbersome and highlycomplicated apparatus required.

The present invention offers a satisfactory solution to the aboveproblem, comprising in essence a rapid and etiicient system forselectively projecting parious characters of afront plate in any desiredsequence onto a photographic member in proper focus at the optical axiswith an absence of distortion and color fringe, and without any motionof the font plate or the associated optical system.

In the accompanying drawings, the invention is shown merely in preferredform and by way of example, and obviously many changes and variationsmay be made within its spirit. It is to be understood, therefore, thatthe invention is not limited to any particular form or embodiment exceptinesofar as such limitations are specied in the claims.

Referring to the drawings:

Fig. l is a diagrammatic view invention;

Fig. 2 is a greatly magnified perspective of a proposed crosseddiffraction grating to be employed inthe present invention; and

Fig. 3 is a diagrammatic view illustrating the projection of one of thecharacters of the font through the diffraction grating.

The apparatus illustrated in the drawings is enclosed in a suitable darkchamber (not shown). In order to eliminate the effects of color fringeon the composed characters, a source of monochromatic light is used tosupply the illumination for the field. The monochromatic light isproduced by passing the light of a standard mercury vapor lamp 1illustrating the present through a standard lter 2 which will transmitonly light in the immediate vicinity of the green line of the mercuryspectrum, that is tosay, in the immediate vicinity of the Wave length5461 Angstrom units. However, any other suitable means for producingmonochromatic light of other Wave lengths may be employed in lieutheerof. The eld light is projected by a condenser lens system 3 upon anarray of characters on a font plate 4.

The array of characters may comprise, as stated, either a plurality oftranslucent characters against an opaque background, or a plurality ofopaque characters against translucent background. The plate 4 may bemade of glass or in the form of a photographic film, or otherwise, withthe characters arranged thereon in vertical and horizontal rows. Inaddition, the plate 4 should be removaile to facilitate the substitutionof characters of different onts.

The characters are adapted to be composed individually in line on aphotographic film 5 by the operation of a keyboard. To this end, anysuitable shutter arrangement may be employed to permit the iield lightto pass through the chosen character. One such possible arrangement isshown in the drawings, comprising a plurality of pivoted horizontal bars6, there being one of such bars for each horizontal row of characters,and a plurality of pivoted vertical bars '7, there being one of suchbars of each vertical row of characters. The operation of a particularkey will, therefore, pivotally displace one bar of each set to uncoverthe particular character associated therewith.

The array of characters 4 is located at the focal plane of a collimatinglens component 8 which renders the light rays coming from the singleexposed character practically parallel. The parallel light rays thenpass through a pair of crossed diffraction gratings 9, constituting themost important component of the present invention.

The diffraction grating is well knownvin the field of optics and may bebrieiiy described as an optical device having a very large number ofparallel and very narrow transmitting or light reecting areas capable ofsetting up wave interference by diffraction, reflection or refraction.Only the former, that is, the transmitting type grating, is shown anddescribed in the present application. However, it should be borne inmind that reection gratings could also be effectively employed with buta few modiiications of the present apparatus. A parallel beam ofmonochromatic light incident upon diifraction gratings of thetransmitting type, due to the Wave-like nature of the light, sets upsecondary wavelets at each of the light transmitting areas, whichwavelets produce interference with wavelets set up by other lighttransmitting areas, giving rise to an interference pattern. When animage of a figure is thus transmitted, by properly focusing theinterference pattern, it is possible to form an entire row of twodimensional images of the gure, and when two gratings are crossed atright angles, it is apparent that this Would add another interferencepattern at right angles to the one caused by the first grating, therebymaking possible the formation of an entire field of images of a givenfigure in two dimensions.

It is this phenomenon, which incidentally may be studied in greaterdetail in any elementary textbook on physics or optics, that makespossible the present invention. As shown in Fig. 2 of the drawings, thecrossed grating 9 herein employed is composed of two individual gratings9a made of some translucent substance, such as collodion, having afurrowed or corrugated surface j consisting of a multiplicity of tinyrounded ridges, there being about 600 to the inch. The gratings 9EL aremounted together back to back, preferably on some light transmittingmember 9b, such as for example a glass plate, in such a manner that thedirection of the ruling of one is at right angles to the direction ofthe ruling of the other. Due to this peculiar construction of thegratings, the crossed rulings form a system of tiny convex lenses, Thislens-like feature of the grating has two advantages over theconventional type grating. For one thing, light ncident upon the systemis better concentrated in the desired direction than in an ordinarygrating system. Also, all, or nearly all, the light incident on thesystem is utilized, none being wasted by conventional absorbing sectionsbetween transmitting slits.

The field light, therefore, creates an image of the single characterselected by the shutter arrangement, and the lightfroml the character soexposed` is divided by the crossed diffraction grating 9 so that asingle` principal image, as well as a .multiplicity of higherorderimages, is formed on' a masking screen 1.1, the images beingfocusedthereon by the .lens-10. The spacing between the images projectedon the masking screen 11 is a `function of the focal length of the lens10and the number of lines per inch of the gratings 92, and the lens 10should be selectedaor corrected so that all the potentially usefulimages will be projected 4in a flat field. lf the spacing betweenthecharacters on the-plate 4 is entirely uniform and equal, the spacingbetween images of the field will not bei-precisely uniformA and equal,although-it will be very nearly rso .(the spacing between lower orderimages differing from the spacing ybetweenhigherorder images by affewthousandths of an inch), but by corrective spacing of the characters onthe plate 4, it is possible to insure that one image of each `of thedifferent selected characters of the array falls along a path ofprojection common to all characters. It is `also possible to employ asquare symmetrical: array of characters and at the same time insurethatk one of the images falls along the common path of projection bycorrective bending of the light rays which form the image to bephotographed. In this way, a symmetrical array of several hundredcharacters can be employed, the central character of the array beinglocated squarely on the optical axis, and a multiplicity of images ofany individually selected character can be created, the number offsuchimages and the spacing between them being so controlled that one imageof the character `will always falll on the optical axis. The maskingscreen `11Qis provided with an aperture 12 located in irwith the opticalaxistto transmit the single image so a mg.

Figure 3 will be helpful in understanding the foregoing explanation. Inthat figure, the principal image A of one of the characters located inthe vicinity of the upper left 4hand portion of the plate 4 (the numeral1 being chosen for purpose of illustration) is shown falling in thevicinity of the lower right hand region of the masking screen 11 afterhaving been projected through the crossed diffraction grating 9. Wellover 50() distinguishable images can be formed about the principal imageA of which the central 400, more or less, will be of practically equalintensity, at least for purposes of printing.

As already explained, while the principal image A merely falls on themasking screen 11, nevertheless one of the plurality of images formedwill always fall on the optical axis and be transmitted through theaperture 12. Thus, a camera focused upon this point can photograph, inturn,each of the characters of the array4 so projected.

The image is thereafter (Fig. 1) projected through a collimating lens 13and reflected by a prism 14 through the imagelenses 15 and 16 onto thephotographic film 5. In the embodiment shown in the drawings, theheavycarriaged photographic film 5 remains stationary while thecomparatively light prism 14 and lenses 15 and 16 are mounted on amovable carriage 17, which latter is adapted to scan the said film 5,moving a set distance after the composition of each character. Themasking screen 11 should be located at the focal plane of thecollimating lens 13, said lens serving to render the rays of lightparallel so that neither focus nor magnification is disturbed by the`movement of the carriage 17. it should be noted that the point size ofthe characters to be composed can be quickly changed by moving the lens16 and the film 5 in the directions indicated by the arrows in Fig. 1.

What is claimed is:

1. In a typographical photocomposing machine, the combination of astationary font plate comprising an array of type characters arranged indifferent positions thereon and in spaced relation to each other, meansfor illuminating any selected type character in the array, a diffractiongrating system for producing, by means of interference of the lightwaves emanating from each different selected character in the array, amultiplicity of images of the selected character, a lens system forfocusing all of said images in a common plane, with one image falling onthe optical axis of the system, a mask located in said plane andcontaining an aperture positioned on the optical axis, said maskpermitting transmission of the light Waves forming the image fal'iing onthe optical axis while preventing transmission of the light wavesforming the other images, and a light sensitive member onto which theprojected images of the different selected characters are recorded, oneafter another, as they `are successively formed at the mask aperture.

2. A combination according to claim 1., including a photographic lenssystem interposed between `the mask and the light sensitive member forlfocusing onto the light sensitive member the images of the differentselected characters as they are successively formed at the maskaperture.

References Cited in the file of this patent UNITED STATES PATENTS1,424,886 Douglass Aug. 8, 1922 1,544,090 Eppenstein June 30, 19251,833,634 Brasse Nov. 24, 1931 1,960,011 Ives May 22, 1934 2,021,162Walton Nov. 19, 1935 2,174,003 Ives Sept. 26, 1939 2,180,417 HuebnerNov. 21, .1939 2,322,602 Terry Iune 22, 1943 FORElGN PATENTS 711,918France July 8, 1931

